I just bought Flower Shop: Winter in Fairbrook but I'm unable to download the demo since my PC says it's "not commonly downloaded and could hurt my computer". Then I't only gives me the optin to delete the demo-file. Please help.

Try disabling any antivirus you're running. There are many POOR antivirus that just to be sure automatically forbid users from downloading new files (that have been updated recently). This is surely one of the cases. Unfortunately I cannot do much except telling them to stop bothering my users, since my files are 100% clean!

Another possible solution is to create a new folder on your computer, then go into the advanced settings on your antivirus program and add that new folder to an 'exceptions' list. Download the game demo file to that folder.
Winterwolves games are great; I wish you success with downloading.